Electrical strain measuring apparatus



Dec. 25, 1951 M, P. VORE ErAL ELECTRICAL STRAIN MEASURING APPARATUS 3 Sheets-Sheet 1 Filed Feb. 11, 1950 w uvm N undo (bugpnaqfnuuou m Que %m m Pe' E k V r. mmm M FllLfllL O- W TNESSES:

Z JSMW ATTORNEY 9 1953 M. P. VORE ET AL 2,579,632

ELECTRICAL STRAIN MEASURING APPARATUS Filed Feb. 11, 1950 5 Sheets-Sheet 2 S5-Posifion 3 S2- Position 1 Comparing A2-B2 2g Fig. 3

Fig.4. Fig. 5. S5- Posifion 4 S2-Posiiion 1 S5- Posiiion5 SE-Posiiion I Q Comparing (E 1 g Comparing Q SS-Posiiion 52-- Position 2 Toidlizing WITNESSES:

INVENTORS Milton P. Vore 8; Maurice J. Gelpi.

ATTORN EY Dec. 25, 1951 M. P. VORE ETAL 2,579,632

ELECTRICAL STRAIN MEASURING APPARATUS Filed Feb. 11, 1950 '3 Sheets-Sheet 3 S2-Posifion 3 55-- Position 2 Comparing C1-C2 WITNESSES: T4 13 T14 INVENTORS Milton P. VOIG. &

Maurice J. Gelpi. Y K,

v ATTORNEY Patented Dec. 25, 1951 ELECTRICAL STRAIN MEASURING APPARATUS Milton P. Vore and Maurice J. Gelpi, Baltimore, Md., assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application February 11, 1950, Serial No. 143,741

Claims.

v This invention relates generally to electrical measuring apparatus, and more in particular to such an apparatus involving a system of electric gauges.

In the weighing of heavy objects such as aircraft, it is frequently necessary to obtain a measurement of the weight within fairly close limits. In the past it has been the practice with a single weighing scale to position the scale beneath the aircrafts wheels, a wheel at a time. The relative magnitudes of the indicated weights then indicates the weight distribution while the sum of the weights serves to indicate the total weight.

However, such a practice is time consuming and since much of the computation is manual, the possibility of errors is high. This invention provides a system of a portable nature involving a plurality of electric gauge units mounted on small platforms as the platform strain detectors. These platforms may be used individually but are preferably employed simultaneously beneath the wheels of an aircraft to be subjected to the load thereof. The gauges are connected in a suitable circuit network whereby the weights may be indicated separately by a suitable switching arrangement in the circuit or the total weight represented in the sum of the gauge outputs indicated.

Alternatively, if portability of the equipment is not required, the electric gauges may be mounted at the four corners of a weighing platform to be subjected to the deflection of the platform supports at the respective points.

In general, this invention is adaptable in the measurement of a multiplicity of forces either individually or simultaneously, to selectively obtain an individual indication of the separate forces or an indication of the combined forces.

A principal object of this invention is to provide an electrical force measuring apparatus which is adaptable for measuring the algebraic sum of a multiplicity of forces or for individually indicating the forces.

It is another object of this invention to provide an electrical force measuring apparatus which is simple in its elements and positive in operation.

More specifically, it is an object of this invention to provide an electrical force measuring apparatus for use in weighing objects involving a plurality of force responsive electric gauge Weighing units used to support the objects being weighed at spaced points in which means are provided responsive to the electrical outputs of the several weighing units for producing an in- 2 dication of each load and/or of the sum of the loads and hence of the total weight bearing upon the Weighing units.

Yet another specific object of this invention is to provide an electric gauging apparatus embodying a plurality of electric gauges responsive to load conditions at predetermined points on a structure in which means are provided for indicating the algebraic sum of the electrical changes of the electric gauges when subjected to load.

The foregoing statements are merely illustrative of the various aims and objects of this invention. Other objects and advantages will become apparent on a study of the following specification, when considered in conjunction with the accompanying drawings, in which:

Figure l is a schematic drawing illustrating an electric gauge of a type employable with this invention;

Fig. 2 is a diagrammatic illustration of a complete weighing equipment embodying the principles of this invention;

Figs. 3 through 9 diagrammatically illustrate the calibrating circuits which are established by the switching equipment and illustrated in Fig. 2; and

Fig. 10 is a diagrammatic illustration of the measuring circuit whereby the outputs of the electrical gauges used in this weighing equipment may be utilized.

Referring now to Fig. 1, the electric gauge generally designated EG is of the form of a magnetic strain gauge which is securely mounted upon a member I which is to be subjected to a load either in tension or compression on bending or torsion. The electric gauge includes a core structure which comprises two E-shaped core members 3 and 4, respectively, which are laminated of sheets of ferromagnetic material. These E-shaped core members 3 and 4 are supported in a bracket 5 of non-magnetic material in a position such that the free extremities of the legs of the respective core sections are disposed in spaced confronting relation. The bracket 5 is securely fastened by means of a bolt 6 to a predetermined point along the strut l. The armature member I of the gauge is also formed of laminated sheets of ferromagnetic material and is positioned by means of a support 8 between the confronting extremities of the E-shaped core members 3 and 4 so that small air gaps are formed therebetween. The support 8 is of the form of a bar which is fastened at one extremity at a point spaced a predetermined distance from the point of fastening of the bracket 5 along the strut I by means of a bolt 9 which threads into the strut. The spacing between the points of fastening of bracket 5 and support 8 along the strut I defines the gauge length and the length of this gauge length for a predetermined loading 'of :the strut 1 :determines the amountof displacement of the armature I with respect to the core members 3 and 4. For the structure illustrated, loading of the strut I in compression reduces the gauge length .of the strain gauge, resulting in movement of the'armature 1 towards the extremities of the E-shaped core member 3 while at the sametime .theaarmature I is moved away fromtheextremities of the E-shaped core member 4 ma like amount. Since the armature member as indicated by the dotted V loops in the magnetic circuitof thegauge-forms part of the flux path for the magnetic flux of the gauge, relative movement of the armature member with respect to the E-shaped core members results in a decreasing .reluc'tanceiof the-flux path including the E-shaped-core member 3 and :an increasing reluctance of the flux :path including the E -shaped core member 4, :and this opposite change in reluctance 'of the separate flux paths- 'of the-gauge is usable :iniproducing an indication of the amountof load which is placed 'upon the strut-l.

In accomplishing this, i the central leg of each E-shaped core memberis provided .with "a winding, winding Ill being associated with E-shaped core :3 and winding 1H :being associated with -E-shape'd core "4. These "Windings are energized with-alternating current,:and with the armature member centrally positioned :so that the reluctances of the-separate flux'paths are equal and assuming equal coil ampereturns, the inductance of "the respective coil circuits-will be the 'same.

However, upon'relative movement of the iarmature member with respect to the coil structure respective magnetic circuits 'are'changed in opposite senses and the coil inductances become unbalanced. This unbalance of inductance is utilizablein 'obtaining'an indication'oftthe loadplaced upon the strut =I To obtain an accurate indication of theload placed supon the :strut 1|, :it :is essential that .the

response 'of the electric *gauge :shall be :a linear function I of the load which is applied to the strut.

In practicing this invention, each weighing platform may comprise a flatupper surface it. This surface will :of course be suitably reinforced 'to carry 'suchloads as may :be placedthereen. and may besupportediupon-a suitable column to pro vide'for mounting of the gauge as'shown in Fig.1.

'These columns orfistruts areinotishcwn inthe interest of simplicity. No attempt has 'beenmade to herein illustrate a* practical platform since the design will depend largely upon the application. 'Thus' it will be appreciated that a load placed upon any one of {the platforms M vwill result in va corresponding compression load on theassociated *column-or strut in an amount depending upon the forceactingonthecolumnin uestion. Four as'previously described, the flux :densities in the I :sion of the respective columns.

tllecolumn'loads is preferably of the null balance type. This obviates the possibility of errors due to the inherent inaccuracies of meters when employed for reading of the actual meter deflection. A circuit of this general type is illustrated in Fig. 2 of United States Patent 2,434,547 which is assigned to thesameassignee as this invention. In this circuit, the coils of the strain gauges are connected in series across a suitable supply of alternating current. This supply is designated by the conductors L! andLZ-ofthe drawings. .Theprimaries of a pair of identical transformers are connected in series and arealso .connectedacross this supply of alternating current, and a parallel circuit is formed byconnecting-the pointbietween the windings of the-coilsof the strain gauge to the point between the iprimary'windings of the associated pair of transformers. With this arrangement, each auge coil has a primary winding of a transformer connected in parallel'therewith. The secondary windings of the transformers are each connected across a full-wave rectifier. The output of each rectifier is loaded by means of a suitable loading resistor, at least one of which is adjustable so that the rectifier output voltages can be made equal. The .rectifiers are connected in adjacent legsoif a conven tional bridge circuit, the remaining two adjacent legs of which are formed by the tapped portions of a vpotenticrneterpand a suitable indicating instrument such as a galvanoineter is connected between the rectifiers on one end and to the-tap of the potentiometer on the other end for the .purpose of measuring the unbalance currents of the bridge circuit.

The'voltage polarities of the rectifiers :as they are connected into this bridge circuit are .such as to be in seriesaround the legs of the bridge. Thus when the rectifier voltages are equal and the bridge is balanced, no current flows through the galvanometer, but upon the occurrence of an unbalance in the rectifier voltages, a current flows through the galvanometer proportional to the difierence in the rectifier voltages. This voltage,'it will be appreciated, is an indication of the relative displacement of the armature and core section of the-strain gauge which in turn is an indication of the deflection of the column, which in its turn is-deflected in anamount proportional to the load applied thereto. As hereinbefore noted, a null balancing type of bridge is preferred. Hence suitable indiciav calibrated in terms of platform load may be provided on a scale adjacent the tap on the bridge balancing potentiometer for the purpose of indicating on the scale the. extent ;of movement of the tap which is necessary to .rebalance the bridge, the bridge being rebalanced when the galvanometer deflection is zero, this indication on the scale will therefore be indication of platform load.

This basic circuithas been expanded in. this invention, to providefor the totalizing of .the outputs .ci a nluralitypf gauges, :each of which mounted in one of a plurality of platformsin the measuring circuit to thereby. indicate the total load upon the weighing platforms. To this end, the strain gauge D has its windings connected in parallel respectively with the primary windings PDI and PD2, respectively, of the transformer DTI and DT2 to form the parallel gauge circuits hereinabove described. In a similar manner, the primary windings PAI and PAZ, respectively, of the transformers ATI and ATZ, and the primary windings PB! and PB2, respectively, of the transformers BTI and BT2, and primary windings PC! and P02, respectively, of the transformers CT! and GT2 are respectively connected in parallel with the corresponding windings of the gauges A, B and C to form the parallel circuits hereinbefore described. All of these parallel gauge circuits are energized by the alternating-current supply of conductors LI and L2. The secondary windings of these transformers which are respectively designated SDI, SD2, SAI, SA2, SBi, SE2, SCI and SC2 are respectively connected across the input terminals of full-Wave rectifiers Dl, D2, Al, A2, Bl, B2, Cl and C2, and corresponding groups of these rectifiers are connected in series in adjacent legs of a measuring bridge circuit so that the corresponding voltages are algebraically added in the adjacent legs.

The means for accomplishing this comprises a pair of drum-type switches designed S2 and S5. The switch S5 includes five operating positions. In postion l, certain circuits are established for connecting the rectifiers in a measuring bridge circuit for the purpose of totalizing the corresponding rectifier voltages. In position 2 of switch S5, circuits are partially established for comparing the side I of each strain gauge circuit with the side II thereof. This comparison is made in the output voltages of the associated pairs of rectifiers. In this connection, the switch S2 is utilized to select the respective pairs of rectifiers which are to be so compared. This comparison through the switch S2 is accomplished in positions 3, 4, 5 and 6 thereof. In position 3 of the switch S5, provision is made for comparing the output voltage of rectifier A2 with the output voltage of rectifier B2. In position 4 of the switch S5, output voltage of rectifier A2 is compared with that of the rectifier C2, and in the last position 5 of the switch S5 the output voltage of the rectifier A2 is compared with that of the rectifier D2.

For the purpose of comparing the rectifier sections as above, the switch S2 is placed in its open position which is pistion No. 1 in which it is illustrated in the drawings. Movement of the switch S5 to position 3 completes a circuit which con- 1 nects the rectifier A2 in a series loop with the rectifier B2 including the galvanometer G-(see Fig. 3). This connection is such that the rectifier voltages are opposed in the series loop. At the same time provision is made for introducing a small balancing voltage to buck the predominant voltage from either of the gauges. This voltage is applied from the tap on the potentiometer R6 which is connected across the alternating current supply conductors LI and L2 through a circuit which includes the rectifier R20, the resistor R4, the potentiometer R6 and an ammeter AM to the opposite side of the line. This circuit may be traced from the positive terminal of the rectifier A2 to the terminal A2a+ on switch segment S5! of the switch S5 to the terminal T5 on this same switch segment. The circuit then continues through the galvanometer and resistor Eli) to the terminal T6 of switch segment S59 on the switch S5 to the terminal TI 6 on this same switch 6 segment. From terminal Tl6, the circuit continues to the reversing switch S6 wherein a tapped portion of resistor R5 may be reversibly inserted into the series loop. From switch S6, the circuit continues to the terminal Tl5 of switch segment S58 on switch S5 to the terminal T9 on the same switch segment, and thence continues to terminal T16 on switch segment S52 to the terminal B2a+ from which the circuit continues to the positive terminal of the rectifier B2. The negative terminals of the rectifiers A2 and B2 are connected together in a circuit which may be traced from the negative terminal of the rectifier A2, to the junction point J I, to the terminal A2aof the switch segment S53, to terminal B2a, to junction point J2 and thence to the negative terminal of the rectifier B2 which completes the series loop. The introduction of the small bucking voltage by means of the reversing switch S6 and the potentiometer R6 makes possible the elimination of the small unbalance of the rectifier voltages. Two identical loads are placed, one on each platform associated with gauge A and B. This load causes a change in voltage ouput of A2 and B2.

Inasmuch as the rectifier A2 is being used as the standard of comparison, adjustment of the variable loading resistor R555 of the rectifier B2 is therefore made in order to balance its voltage against that of the rectifier A2 in the series loop. This procedure results in equal voltage changes at the output of A2 and B2 for the application of equal load changes and will be evidenced by no galvanometer movement as the load on platforms A and B is varied in equal amounts.

Upon completion of this comparison of rectifiers A2 and E2, the switch S5 is moved to position 4 which compares rectifier A2 with rectifier C2 in a circuit similar to that hereinabove discussed. This circuit is illustrated in Fig. 4 and is traced from the positive terminal of the rectifier A2, to the terminal AZa-I- of switch segment S5 to the terminal T5 through the galvanometer G and resistor Bill, to terminal T6 on the switch segment S59, to terminal Tic also on this switch segment. The circuit then continues through the reversing switch S5, to terminal T15 on switch segment S58, to terminal T9 on the same switch segment, to terminal TI 5 on switch segment S52, to terminal C2a+ on this same switch segment, and thence the circuit continues to the positive terminal of rectifier C2. The negative terminals of rectifiers A2 and C2 are connected together in a circuit traceable from the negative terminal of rectifier A2, to junction point J I, to terminal A2a on switch segment S53, to the other terminal C2aon this same switch segment to junction point J3 and thence to the negative terminal of rectifier C2 to complete the series loop. Balancing of the circuit after introduction of the small bucking voltage is accomplished in this instance by adjustment of loading resistor Rtis in a manner similar to that described for 'A2 and B2.

In the first position of the switch S5, which condition is illustrated in Fig. 5, the rectifier D2 is compared with rectifier in a circuit traceterminal T6 on switch segment S58; to the other terminal Tit on this switch segment, to the reversing switch S6 to the terminal TI 5 on switch segment S58, to terminal T9 on this switch segenhance -ment,:to terminal 'Tl ll onswitch ssegment 852; to terminal .D2a+- on this :switch segment and thence to the positive" terminal of the rectifier D2. The negative'terminals of the rectifier are joined in a circuit traceable from the negative terminalof rectifier 2,110 junction point J-l to terminal =A2aof switch segment S53, to terminal 'D2a.- on this switch segment and thence to the negative "terminal of the rectifier D2.

Having compared the "rectifiers B2, C2 and D2 with the rectifier 1A2, the calibration may be completed by comparing the side I of each measuringscircuit with the side II thereof. This may be accomplished by comparing the rectifier volt- :ages, forinstance the voltage ofrrectifier Cl with that of G2, etc. Thus for Lgivenz-settings of .a single gaugathe-voltages of corresponding rectifiersmay be made-equal, and since the-number I-I sides of thenetworks have beencompared :have been calibrated and ready for use.

This second step in the calibration is obtained bypositioning theswitch 85in its position 2 and thereafter successively positioning the switch S2 i -in .its positions 3 through B. ,In position 3, as illustrated in Fig. 6, the rectifier C! is connected a, series loop with the rectifier C2, the rectifier voltages being-opposed in this loop. In position 4. the circuit includes :the rectifiers Bi and B2 in oppcsitioni-n the series loop. This is illustrated iii-Fig. 1. In Fig. 8, in position 5 of S2, rectifiers Al .and A2 -are compared, and in Fig. 9, position 5 of switch-S2 forms a loop circuit in which the rectifiers DI and D2 are compared,

Returning now to Fig. 6 and also to Fig. 2, itshould be noted that the measuring circuit in which the rectifiers are connected includes a potentiometer .circuit in which the units of :matched pairs of potentiometers are connected ,on opposite sides of the null balancing potentiometer RIB. These potentiometers and the null balancing ipotentiometers are connected in series circuitrelation and the units of one pair are designated RNA and RUB, the movable taps of which are connected mechanically as indicated by the dotted line. Units RIZA and RlZB are also mechanically ganged asshown by the dotted lines so that the tape thereof aremoved simul taneously. The pair of potentiometers RI M. and =RI1IB are arranged so that upon actuation'of the mechanical connection, for instance clockwise as viewediin Fig. 2. The resistance of the potentiometer RNA is decreased while that of the potentiometer RUB is increased. In the. case of the remaining potentiometers RNA and RI2B, the electrical connections are such that upon movement of the mechanical connection therebetween, the resistances of these potentiometers change :in the same direction, that is, the resistances increase or decrease simultaneously. With anarrangement'suchas this, the upper and lower ends'fof :the indicating scale .29 are conveniently adjusted. In the following ,:-sequence :Ioi tests, lRHA, .HB, lZ-A, 12B and'Rl3-are ileft Fin fixed positions throughout.

:In position 3 of switch S2 and position 210i switch St, the circuit connecting the rectifiers Ci :andCZin opposition across the potentiometer circuit may be traced from the terminal T4 on ronenndzof epotentiometer RNA to terminal Tllb on switch .segment S24, through the switch segmencszr 'ltO the terminal 'Cl.-|-.,' on this switch Pscgment to zjunction point J 4, {and thence :to the positive terminal :of the rectifier Cl. From the so andimade equal, the entire system will then negative terminal of rectifier C2 l, the circuit continues to terminal CI on switch segment. S22, to the terminal T13 on this switch segment, .to terminal T112 on switch segment SZL'tOterminal C2bon this same switch segment'and thence to the negative side of the rectifier C2. From thepositive side of rectifier C2, the-circuit continues to junction point J5, to terminal C2b+ on switch segment $23, to terminal Tl lb on this switch segment and thence to the terminal TM on the end of potentiometer R! IB which completes the series loopincluding-the potentiometer circuit. It willbe noted that rectifiers Cl and C2 are connected in voltage opposition .in this circuit- The galvanometer'G is connected across the potentiometer circuit between terminals T4?) and T14 in :a circuit which is traceable from terminal TM) over conductor CM, to terminal Tea on switch segment 8.51 of. the switchzSE, to terminal T5 on :switch segment 85!, through the galvanometer G and resistor Bill to terminal T5 on switch segment. S52, :to terminal .Tl' on this switch segment, to terminal T8 onswitch segment S53, to terminal Tit on thisswitch segment, to terminal Till .onswitch segment -85 2, to terminal Z on this switch segment. The circuit continues through the tapped portion of potentiometer R6 which .is grounded on theside of terminal '1! (see Fig. 2). Inasmuch ,as the circuit connecting with the terminal Tl-5b at the potentiometer R! IB is grounded .(see Fig. 2'), it willbe appreciated that the galvanometer circuit is completed across the potentiometer circuit through ground and this completed circuit is shown in Figs. 6 through-9. The balancing voltage which -is tapped from resistor R6 is applied in the galvanometer circuit in opposition to the voltage of the rectifier Cl and the reversing switch S6 is not employed for the purpose of switching the polarity of this voltage. A load is now placed on the platform'supported-bycolumn C.after the artificial :zero is set through R6. R?! 5 is then changed until the galvanometer reads zero. Thus the comparison of Cl toCZ is complete since any load on platform C produces equal voltage changes in C I andCZ.

This is-done for A, B, :C and Dplatforms and since the II sides of each were previously set and the I sides'are now adjusted to 'meet them, both sides of all gauges are matched.

.In Fig. v"l, the calibrating circuit for the rectiiiers B1 and B2 is traceable from the terminal T4 at potentiometer RNA to terminal .Tt'b on .switchsegment S24, through switchsegment S24 to the terminal Bl which is connected to switch segment S-Zd in the number 4 position of the switch S2. The circuit continues to junction point J6 and thence to the positive "terminalcf the rectifier Bl. From the negative terminal of rectifier B! the circuit continues to terminal 13! on switchsegment S22, to terminal Tl3 on this switch segment, to terminal T12 on switch :segment :Stiyto terminal 132bon'this switch segment and thence to the negative side ofirectifier B2. .From'the positive side of rectifierBZ, the circuit is "traced -:to junction point Jlto terminal B2 b+ of switch segmentS23, to terminal 'IMb on this switch segment, to terminal TM at the end of potentiometer RHB. The galvanometer circuit is connected across the potentiometer circuit in exactly thesame manner ascdescribedin'Fig. 6.

' In Fig. '3, .-illustrating the number 5 ,:position a :of, the :switch S2, :the calibrating circuit'for the rectifierssAl and =A21i$ tracedfrom the :terminal T4 at potentiometer RIIA, to terminal T4b on switch segment S24, to terminal AI+ on this switch segment, to junction point J8 and thence to the positive side of rectifier AI. From the negative side of rectifier Al the circuit continues to terminal AI- on switch segment S22, to terminal TI3 on this switch segment, to terminal TI 2 on switch segment S2I, to terminal A2b on this switch segment and thence to the negative side of rectifier A2. From the positive side of rectifier A2, the circuit is traced to junction point J9, to terminal A2b+ on switch segment S23, to terminal TI 4b on this switch segment, to terminal TM on potentiometer RI IE to complete the loop circuit. The galvanometer circuit is again traced as described in Fig. 6.

In position 6 of the switch S2, the calibrating circuit for rectifiers Di and D2 is traced from terminal T4 at potentiometer RI IA, to terminal T4b on switch segment S24, to terminal DI+ on this switch segment and thence to the positive side of rectifier DI. From the negative side of rectifier DI, the circuit continues to DI on switch segment S22, to terminal TI3 on this switch segment, to terminal TI2 on switch segment S2 I, to terminal DZbon this switch segment, to junction point J I and thence to the negative side of rectifier D2. From the positive side of rectifier D2, the circuit continues to junction point J Iii, to terminal D2b+ on switch segment S23, to terminal TMb on this switch segment and thence to terminal TI4 on potentiometer RIIB to complete the loop circuit. Again the galvanometer circuit is the same as that traced in Fig. 6.

For establishing the totalizing circuits to indicate the algebraic sum of the voltages of the corresponding rectifiers in the measuring system, the switch S5 is placed in position I and the switch S2 moved to position 2 which is its totalizing position. In this position of the switches, as shown in Fig. 10, the rectifiers DI, Al, BI, CI are connected in series in one leg of the measuring bridge circuit. The rectifiers D2, C2, B2 and A2 are connected in series in an adjacent leg of the measuring bridge circuit, the remaining two adjacent legs of which are determined by the tapped portions of the potentiometer circuit including the potentiometers RI IA, RIZA, RI3, RI2B and Ri IB. In this connection of the rectifiers, the rectifier voltages are in series around the legs of the bridge circuit and the galvanometer circuit is connected across the galvanometer terminals of the bridge between the negative terminal of rectifier CI and the positive terminal of rectifier A2 on one side and to the tap T3 of potentiometer RIB on the other side. Tracing this circuit around the legs of the measuring bridge circuit and beginning at the positive terminal of rectifier DI, the circuit continues to junction point J25, to terminal TI+ of switch segment S24, to terminal T41) on this switch segment, to terminal T4 of potentiometer RIIA, through potentiometer RIIA, through potentiometer RIZA, through potentiometer Rlii, through potentiometer RI2B, through potentiometer RIIB, to terminal TIflb on switch segment S23, to terminal TZIb-lon this switch segment, to terminal T2a+ on switch segment S51, to therminal D2- on this same switch segment, to junction point J23 and thence to the negative side of rectifier D2. From the positive side of rectifier D2, the circuit continues to junction J 22, to terminal D2+ on switch segment S56, to terminal C2 on this switch segment, to junc- 10 tion point J 2i and thence to the negative side of rectifier C2. From the positive side of rectifier C2, the circuit is traceable to junction point J20, to terminal 02+ of switch segment $54, to terminal 32- on this switch segment, to junction point J I9 and thence to the negative side of rectifier B2. From the positive side of rectifier B2, the circuit continues to junction point J I 8, to terminal B2+ on switch segment S55, to terminal A2- on this switch segment, to junction point J ii and thence to the negative side of rectifier A2. From the positive side of rectifier A2, the circuit continues to junction point J I6, to terminal T2 on switch segment S2I, to terminal TI2 on this switch segment, to terminal TI3 on switch segment S22, to terminal TI- on this switch segment, to junction point J I 5 and thence to the negative side of rectifier CI. From the positive side of rectifier CI the circuit continues to junction point J4, to junction point J I4 and to the negative side of rectifier BI. From the positive side of rectifier BI the circuit continues to junction point J6, to junction point J I3 and to the negative side of rectifier AI. From the positive side of rectifier Al the circuit continues to junction point J 8, to junction point J I2 and to the negative side of rectifier DI which completes the path around the legs of the bridge circuit.

The galvanometer circuit is traceable from terminal TI 2 on switch segment S21, to terminal TH on switch segment S52, to terminal TIE} on this switch segment, to terminal T9 on switch segment S58, to terminal T8 on this switch segment, to terminal T! on switch segment S59, to terminal T6 on this switch segment through resistor Rlfl and galvanometer G to terminal T5 on switch segment S5I, to terminal TBa on this switch segment and to terminal or tap T31) on potentiometer RI3. By reference to Fig. 10, it will be noted that the voltages of the corresponding rectifiers are in series in their respective legs of the bridge circuit and that the total voltage of the rectifiers is in series around the legs of the bridge circuit. Thus it will be appreciated that with the bridge II balanced, equal total rectifier voltages in the adjacent rectifier legs of the bridge result in zero current fiow through the galvanometer circuit, but upon the occurrence of an unbalance of the voltages in the adjacent legs of the bridge, a voltage is impressed across the galvanometer circuit having a current which is proportional to the magnitude of the voltage unbalance. Since this voltage unbalance as previously noted is a linear function of the load placed upon the weighing platform I4, it will be appreciated that the galvanometer will be energized by a current which is proportional to the load being measured. To obviate the inherent inaccuracies of a deflection type of measuring system, the tap of the potentiometer RIS is adjusted to restore the bridge circuit to a balanced condition. In so doing, the pointer P is moved along the scale 20 which may be conveniently calibrated in pounds and therefore the indication read directly from the scale gives the actual weight in pounds of the load supported on the weighing platform I4. This direct reading is done by setting RI IA, RI IB for zero and RIZA, RIZB for a definite reading of dial 20 on RI3 when some definite load is applied to the platforms.

While but one embodiment of this invention has been illustrated, it will be appreciated by those skilled in the art that numerous variations in details as well as application of the disclosed subject matter may be made without departing from the spirit and scope of this invention. It is, therefore, intended that the foregoing dis-. closure and the showings made in the drawings shall-be considered only asillustrative of the the principles of this invention and not construed in a limiting sense.

We claim as our invention:

1. Apparatus responsive to the sum of the strains of at least two elements subject to stress comprising, in combination, at least two electric strain gauges, one for each of said elements; means securing said electric strain gauges to respond to the stress of the corresponding one of said elements, each of said strain gauges comprising a pair of electrical circuits and means responsive to the strain of its element for controlling the electrical characteristics of the cir cuits, said circuits being electrically balanced for a given strain in the corresponding element and being unbalanced by the strain responsive means upon the occurrence of strain in its element differe'nt from the given strain, unidirectional voltage producing means connected with each electrical circuit of each electric strain gauge, the unidirectional voltage producing means for each gauge producing opposed voltages, a bridge circuit including corresponding unidirectional voltage producing means of each electric strain gauge in series in adjacent legs thereof, and circuit means responsive to the unbalance of said bridge circuit.

2. Apparatus responsive to the sum of the strains of at least two elements comprising, in combination, at least a pair of electric gauges one for each element, each having a pair of electric circuits, means forming a part of each electric gauge responsive to the strain of the corresponding element for oppositely varying the electrical characteristics of the associated pair of electric circuits, circuit means for energizing the electric circuits, rectifier means connected with each electric circuit of each electric gauge for producing unidirectional voltages varying in dependence of the change in electrical characteristic of the associatedv electric circuit, the pair of rectifiers connected with each electric gauge producing opposed vo1tages, circuit means con-- necting the corresponding rectifier means of each electric gauge in series forming a pair of series rectifier circuits having opposed voltages, a bridge circuit including the pair of series rectifier circuits in adjacent legs, and circuit means responsive to the electrical output of thefbridge circuit.

3. In combination, at least two electricgauges,

each having a air-oicoilsand a movable armature for oppositely varying the coil voltages, circuit means for supplying alternating current to the coils of each electric gauge, a rectifier connected across each coil of each electric gauge, the rectifiers connected across the coils of each electric gauge producing opposed voltages, circuit means connecting the corresponding rectie fiers of each electric gauge in series forming two series. connected rectifier circuits, a bridge circuit including the series connected, rectifier circuits in adjacent legs, and circuit means responsive to the electrical output of the bridge circuit.

4.,In an electricv gauge system, the combination of, a plurality of alternating-current elec-. tric gauges, each having a pair of opposed alternating current output, circuits; a plurality of rectifiers, one connected with each alternating current output circuit, first circuit means connecting corresponding rectifiers in series circuit relation so that half the total number of rectifiers are connected in series in said first circuit means, second circuit means connecting the remaining rectifiers in series circuit relation, and circuit means responsive to the difierence of voltage of the first and second circuit means.

5. In anelectric gauge system, the combination of, a plurality of alternating-current electric gauges, each having a pair of opposed alternating-current output circuits; a plurality of rectifiers one connected with each alternating-current output circuit, first circuit means connecting corresponding rectifiers in series circuit relation so that half the total number of rectifiers are connected in series in said first circuit means, second circuit means connecting the remaining rectifiers in series circuit relation, an electrical bridge circuit including said first and said second circuit means in adjacent legs thereof, and circuit means responsive to the electrical unbalance of said bridge circuit.

MILTON P. VORE. MAURICE J. GELPI.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,421,626 Kuehni- June 3, 1947 2,443,098 Dean June 8, 1948 2,470,069 Davies May 10, 1949 2,478,720 Sourwine et al. Aug. 9, 1949 2,540,807 Berry Feb. 6, 1951 

